Field of the Invention
The present invention generally relates to the field of household appliances for laundry and garments treatment. In particular, the present invention relates to appliances for drying laundry, such as laundry dryers and combined washers/dryers.
Discussion of the Related Art
Appliances for drying laundry are adapted to dry clothes, garments, laundry in general, by circulating hot, dry air within a tumbler or drum. The drum is rotatable within a machine external casing or cabinet, and is designed to contain the items to be dried. The rotation of the drum causes agitation (tumbling) of the items to be dried, while they are hit by the drying air flow.
Combined laundry washer/dryer appliances combine the features of a washing machine with those of a dryer. In a washer/dryer, the drum is rotatable within a washing tub which is accommodated within a machine external casing or cabinet.
In a known type of laundry dryers and washers/dryers, also referred to as “condenser dryer”, the drying air flow is typically caused to pass through the drum, exiting therefrom from a drying air outlet, then it passes through a moisture condensing system, where the humid, moisture-laden air is at least partially dehydrated, dried, and the dried air flow is heated up by means of a heating arrangement; the heated drying air flow then re-enters into, and passes again through the drum, and repeats the cycle.
While in some known condenser laundry dryers and washers/dryers the moisture condensing system is an air-air heat exchanger, exploiting air taken in from the outside for cooling down the drying air (and thus cause the condensation of the moisture), other known dryers and washers/dryers exploit a heat pump to dehydrate the drying air flow. In these “heat pump dryers”, the heating of the drying air may be performed by the heat pump itself. An example of heat pump laundry dryer can be found in EP 2270276.
DE 4304226 discloses a condensation tumble dryer, comprising a heat pump, and an air circuit in which the airstream is guided for heating over the liquefier of the heat pump and subsequently into an air inlet of a drying chamber containing the drying items, and in which the airstream is guided for cooling out of an air outlet of the drying chamber at least partly over a heat exchanger containing the evaporator of the heat pump. In order to achieve a faster heat up of the process airstream, a second heating apparatus in the form of an electric resistance heating is disposed between the process air fan and the air inlet of the drying chamber. This resistance heating can be switched on and off by a switch which is actuated by the electronic program control. The resistance heating is switched off when the pressure of the cooling agent exceeds a critical value during the drying phase. For this purpose, a temperature sensor is arranged on the connecting tube between compressor and liquefier, which sensor monitors the temperature which is proportional to the pressure of the cooling agent.